1. Field of the Invention
This invention relates to improvements in internal combustion engines of the split type operable on less than all of its cylinders when the engine load is below a given value.
2. Description of the Prior Art
It is known and desirable to increase the efficiency of a multicylinder internal combustion engine by reducing the number of cylinders on which the engine operates under predetermined engine operating conditions, particularly conditions of low engine load. Control systems have already been proposed which disable a number of cylinders in a multicylinder internal combustion engine by suppressing the supply of fuel to certain cylinders or by preventing the operation of the intake and exhaust valves of selected cylinders. Under given load conditions, the disablement of some of the cylinders of the engine increases the load on those remaining in operation and, as a result, the energy conversion efficiency is increased.
It is common practice to introduce exhaust gases into the disabled cylinders through an EGR valve adapted to open under given load conditions and to prevent the introduced exhaust gases from flowing to the cylinders remaining in operation by the use of a stop valve adapted to close in timed relation with the opening of the EGR valve. This is effective to suppress pumping loss in the disabled cylinders and attain higher fuel economy.
One difficulty with such split type internal combustion engine is the tendency to cause imperfect combustion and to produce a great amount of unburned exhaust components should any trouble occurs with engine components such as EGR or stop valves. The unburned components flow into the catalytic converter provided in the exhaust system and react therein to overheat the catalytic converter. This results in a severe reduction of the service life of the catalytic converter.
The present invention provides an improved split type internal combustion engine equipped with a safety means for keeping the catalytic converter from overheating if trouble occurs with certain engine components such as EGR or stop valves.